Nanofibers are ultrafine filament substances with seemingly unlimited marketplace applications. These highly versatile filaments can be produced artificially though electrospinning—a process that uses an electrical charge to draw nanofibers from a polymer solution. The standard electrospinning device setup consists of a spinneret (typically a syringe needle) connected to a high-voltage (5 to 50 kV) direct current power supply, a syringe pump, and a grounded collector. A polymer solution is loaded into the syringe and this liquid is extruded from the needle tip at a constant rate by a syringe pump.
Conventional electrospinning procedure results in dense two-dimensional (2D) fibrous mat that are collected over time, giving rise to compact structure with small pore size that inhibits cell infiltration and proliferation1;2. These densely packed layers of nanofibers have only a superficially porous network and form a sheet-like microstructure. This unavoidable characteristic restricts cell infiltration and growth through the entire layers of nanofiber scaffolds.
In order to architecture three-dimensional (3D) nanofibrous scaffolds with lower density and larger pore size, numerous approaches have been attempted3;4, including the incorporation of nanoparticles, using larger microfibers, or removing embedded salt or water-soluble fibers to increase porosity.
Some basic parameters that govern electrospinning process, such as electric charge, external force on spinneret jet, magnetic field5 have been investigated for promoting 3D fibers architecture. However, it has been demonstrated that collection method acts most effectively on constructing 3D fibers and manipulating elaborate fibrous structure6. Advanced collection techniques, such as wet electrospinning7, rolling or stacking collectors8-10, and yarn11 have shown to be eligible for 3D nanofiber fabrication. From designing various geometrical collectors instead of the conventional parallel-plate collectors, it's possible to produce 3D nanofibers scaffold in certain shapes.
Overall, all current strategies to create electrospun scaffolds collect nanofibers in an unfocused, planar manner, which causes subsequent layers to adopt a densely packed network and prevents the formation of three dimensional structures with good stability. To overcome this limitation, we invented an automatic nanofiber collector device to control the porosity, pore size, crystallinity, geometry and the number of the layers and/or thickness of formed nanofibers.
The design of the automatic nanofiber collector device is consists of (1) a collector platform; (2) a non-conductive device used to fix the collector device; (3) a plurality of electro-conductive wires or needles being pierced through the collector platform with the same or various heights, and (4) the ends of the needles (at bottom) are wired and controlled by a microcontroller, providing forward, stand and backward movements for attached needles.
This automatic nanofiber collector device is specially designed by embedding an array of electro-conductive needles in a flat surface. The terminals of the needle are wired and controlled by micro-steppler controller. The micro-stepper is programmed to control individual needle movement (forward, backward and still at desired moving velocity).
Nanofibers are allowed to accumulate throughout the electrospinning process and then removed manually or automatically. The mechanism behind nanofiber accumulation is that a corona discharge is formed during electrospinning when the heights of pierced needles varies, enabling the gradual built-up of electrospun nanofibers on the collector and eventual formation of 3D bulk nanofiber scaffold.
The desired structure of the 3D nanofiber scaffold can be tailored by the micro-stepper motor controller by changing the pattern and velocity of needle movement, generalized or selective needles movements, as well as intermittent versus continuous movement.
This automatic nanofiber collection device can be used alone (single electrospinning) or by simultaneous incorporating (spray, co-electrospinning or 3D plotting/plasma spraying or other applicable loading methods) of other biomaterials (biopolymers, bioceramics, bio-conjugates, etc.), biomolecules, ions (trace elements), viable cells (stem cells or differentiated cells), to form desired 3D nanofiber matrix composites (Sandwich, layer-by-layer, gradient models, and thereof).
The potential application of this new technology includes, but not limited to, the tissue engineering of soft and hard tissues, and controllable drug delivery.
The desired 3D structure of nanofiber scaffold can be tailored by changing the pattern and velocity of collector surface needle movement programmed by a micro-stepped motor controller.
One of the unique characters of automatic nanofiber collector device is that a corona discharge effect is applied as the mechanism of collecting nanofibers throughout the heads of the needles. By controlling the movement of the aligned needles, nanofibers continue to build up along the needle heads concurrently. This new method extended the application of the electrospinning techniques in providing 3D nanofibrous scaffold in both soft tissue and bone tissue engineering, among other potential biological or industrial applications.
Ho-Wook Jun et al., (U.S. Pat. No. 0,250,308 A1) disclose the use of different geometric collectors with fixed electrodes to produce 3D electrospun nanofibers. The inventors focus on designing of geometries of non-conductive distal end plate without considering the movements of electrodes.
Mohammadi Yousef, et al., (Euro Pat. No. EP2045375 (B1)), disclose the design of rotating collector, which consists of multiple electrodes-formed cylindrical cages, to produce 2D or 3D electrospun nanofibers with alignment.
Vince Beachley et al. (U.S. Pat. No. 7,828,539) disclose the design of two parallel conducting plates with rotating tracks to align the fibers and distribute the fibers into 3D fiber mesh.
In most tissues, cells are embedded in the entangled extracellular matrix network (ECM). Proper cell phenotype is of particular importance in regulating matrix biosynthesis and remodeling. It is evident that spatial arrangement of cells embedded in ECM has a great effect on the phenotypic fate of these cells. The interactions between cells and cell-matrix both play an important role by regulating different gene expression. The micro scale contact and communication between cells and cues from the matrix cause sequential intracellular events to influence cellular behavior.
Fabrication of 3D nanofiber scaffold with programmed spatial control of cell deposition is challenging. Many efforts have been made in recent years in developing and testing printing techniques including those based on laser pulses, inkjets and other more novel approaches1213;1415. Valve-based printing techniques are one of the newest additions to this list and have the advantage of being one of the gentlest techniques for printing any number of cells but, as with all other nozzle-based techniques, clogging is potentially an issue16;17.
We developed a new cell printing platform that is capable of depositing cells with precise quantity and high cellular viability. The combined methods of electrospun 3D nanofiber matrix with layer by layer based cell deposition systems were used for the controllable and repeatable creation of uniform 3D nanofiber matrix with desired multilayer deposit of viable cells. It can be a single nozzle system18 or dual nozzle system19.